1. Field of the Invention
This invention relates to an image processing apparatus, and more particularly, to an image processing apparatus for decoding encoded data subjected to motion-compensation predictive encoding.
2. Description of the Related Art
Recently, in the field of digital transmission of moving images, high-efficiency encoding techniques have been intensively studied, and "image-encoding/decoding apparatuses using motion-compensation predictive encoding", in which excellent image transmission can be performed even at low data rates, have been realized.
In such an apparatus, a digitized image signal is first subjected to high-efficiency encoding at the transmission side for performing encoding, so that the amount of information is compressed and reduced.
Motion-compensation predictive encoding is adopted as the encoding method for the apparatus in order to improve the encoding efficiency. Motion information, including motion vectors, and encoded data are obtained in this processing.
The motion information and the encoded data are subjected to error correction encoding by adding parity bits thereto, and are transmitted to the reception side for performing decoding via a transmission channel. At the reception side, error correction for codes having the parity bits is performed for the received data string, and the resultant data is input to a high-efficiency decoding circuit.
The high-efficiency decoding circuit expands the amount of information of the received data in order to return the data to the original digital image signal, which is converted into an analog image signal, and the analog image signal is output.
When all errors produced in the transmission channel cannot be completely corrected by error correction processing at the reception side, the above-described high-efficiency decoding circuit cannot exactly decode image data if an uncorrectable error is present in either the motion information or the encoded data. In such a case, degradation in the reproduced image is minimized by replacing the corresponding image data by corrected data (which may comprise concealed data from another frame) and outputting the concealed data. More specifically, the image data is concealed, for example, by being replaced by image data in the immediately preceding field or frame.
However, in the conventional method of decoding image data at the reception side of the above-described high-efficiency encoding/decoding apparatus, even if an uncorrectable error is produced only in encoded data, all data including motion information, in which no uncorrectable error is present, are abandoned, so that a concealed portion becomes, in some cases, more pronounced in a moving portion in the image, thereby degrading the quality of the reproduced image.